Object detecting device and information acquiring device

ABSTRACT

An information acquiring device has a light source which emits light of a predetermined wavelength band; a projection optical system which projects the light emitted from the light source toward the target area with a predetermined dot pattern; and a light receiving element which receives reflected light reflected on the target area for outputting a signal. In this arrangement, the projection optical system projects the light toward the target area in such a manner that a dot of a reference pattern of the light to be received by the light receiving element has a pitch equal to or larger than 2.5 pixels at least in an alignment direction in which the light source and the light receiving element are aligned.

This application claims priority under 35 U.S.C. Section 119 of JapanesePatent Application No. 2010-217975 filed Sep. 28, 2010, entitled “OBJECTDETECTING DEVICE AND INFORMATION ACQUIRING DEVICE” and Japanese PatentApplication No. 2011-116703 filed May 25, 2011, entitled “OBJECTDETECTING DEVICE AND INFORMATION ACQUIRING DEVICE”. The disclosures ofthe above applications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an object detecting device fordetecting an object in a target area, based on a state of reflectedlight when light is projected onto the target area, and an informationacquiring device incorporated with the object detecting device.

2. Disclosure of Related Art

Conventionally, there has been developed an object detecting deviceusing light in various fields. An object detecting device incorporatedwith a so-called distance image sensor is operable to detect not only atwo-dimensional image on a two-dimensional plane but also a depthwiseshape or a movement of an object to be detected. In such an objectdetecting device, light in a predetermined wavelength band is projectedfrom a laser light source or an LED (Light Emitting Diode) onto a targetarea, and light reflected on the target area is received by a lightreceiving element such as a CMOS image sensor. Various types of sensorsare known as the distance image sensor.

A distance image sensor configured to scan a target area with laserlight having a predetermined dot pattern is operable to receive a dotpattern reflected on the target area on an image sensor for detecting adistance to each portion of an object to be detected, based on a lightreceiving position of the dot pattern on the image sensor, using atriangulation method (see e.g. pp. 1279-1280, the 19th Annual ConferenceProceedings (Sep. 18-20, 2001) by the Robotics Society of Japan).

In the above method, for instance, laser light having a dot pattern isemitted in a state that a reflection plane is disposed at a positionaway from an irradiation portion of laser light by a certain distance,and the dot pattern of laser light irradiated onto the image sensor isretained as a template. Then, a matching operation is performed betweena dot pattern of laser light irradiated onto the image sensor at thetime of actual measurement, and the dot pattern retained in the templatefor detecting to which position on the dot pattern at the time of actualmeasurement, a segment area set on the dot pattern of the template hasmoved. The distance to each portion, in the target area, correspondingto each segment area, is calculated, based on the moving amount.

In the object detecting device thus constructed, at the time of actualmeasurement, a dot of laser light may be irradiated onto the imagesensor in a state that the dot overlaps a plurality of pixels on theimage sensor. In such a case, signals may be concurrently outputted fromthe pixels adjacent to each other, onto which the dot has beenconcurrently irradiated. As a result, in a dot pattern to be obtainedbased on an output from the image sensor, some borderlines between dotsmay not be discriminated as a whole. Thus, it may be impossible toperform a matching operation between a dot pattern of laser lightirradiated onto the image sensor at the time of actual measurement, andthe dot pattern retained in the template. As a result, detectionprecision of a distance to each portion of an object to be detected maybe lowered.

SUMMARY OF THE INVENTION

A first aspect of the invention is directed to an information acquiringdevice for acquiring information on a target area using light. Theinformation acquiring device according to the first aspect includes alight source which emits light of a predetermined wavelength band; aprojection optical system which projects the light emitted from thelight source toward the target area with a predetermined dot pattern;and a light receiving element which receives reflected light reflectedon the target area for outputting a signal. In this arrangement, theprojection optical system projects the light toward the target area insuch a manner that a dot of a reference pattern of the light to bereceived by the light receiving element has a pitch equal to or largerthan 2.5 pixels at least in an alignment direction in which the lightsource and the light receiving element are aligned.

A second aspect of the invention is directed to an object detectingdevice. The object detecting device according to the second aspect hasthe information acquiring device according to the first aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, and novel features of the present inventionwill become more apparent upon reading the following detaileddescription of the embodiment along with the accompanying drawings.

FIG. 1 is a diagram showing an arrangement of an object detecting deviceembodying the invention.

FIG. 2 is a diagram showing an arrangement of an information acquiringdevice and an information processing device in the embodiment.

FIGS. 3A and 3B are diagrams respectively showing an irradiation stateof laser light onto a target area, and a light receiving state of laserlight on an image sensor in the embodiment.

FIGS. 4A and 4B are diagrams for describing a reference template settingmethod in the embodiment.

FIGS. 5A through 5C are diagrams for describing a distance detectingmethod in the embodiment.

FIGS. 6A through 6F are diagrams for describing a drawback to beinvolved in the case where the pitch of a dot is equal to 2 pixels.

FIGS. 7A through 7F are diagrams for describing a drawback to beinvolved in the case where the pitch of a dot is equal to 2 pixels orsmaller.

FIGS. 8A through 8F are diagrams showing a dot pattern setting method inthe embodiment.

FIGS. 9A through 9F are diagrams showing another dot pattern settingmethod in the embodiment.

FIGS. 10A through 10F are diagrams showing yet another dot patternsetting method in the embodiment.

FIGS. 11A through 11F are diagrams showing still another dot patternsetting method in the embodiment.

The drawings are provided mainly for describing the present invention,and do not limit the scope of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

In the following, an embodiment of the invention is described referringto the drawings. The embodiment is an example, wherein the invention isapplied to an information acquiring device which is configured toirradiate a target area with laser light having a predetermined dotpattern.

In the embodiment, a laser light source 111 corresponds to a “lightsource” in the claims. A projection optical system 11 (a collimator lens112, an aperture 113, a DOE 114) correspond to a “projection opticalsystem” in the claims. A CMOS image sensor 124 corresponds to a “lightreceiving element” in the claims. The description regarding thecorrespondence between the claims and the embodiment is merely anexample, and the claims are not limited by the description of theembodiment.

Firstly, a schematic arrangement of an object detecting device accordingto the first embodiment is described. As shown in FIG. 1, the objectdetecting device is provided with an information acquiring device 1, andan information processing device 2. ATV 3 is controlled by a signal fromthe information processing device 2.

The information acquiring device 1 projects infrared light to theentirety of a target area, and receives reflected light from the targetarea by a CMOS image sensor to thereby acquire a distance (hereinafter,called as “three-dimensional distance information”) to each part of anobject in the target area. The acquired three-dimensional distanceinformation is transmitted to the information processing device 2through a cable 4.

The information processing device 2 is e.g. a controller for controllinga TV or a game machine, or a personal computer. The informationprocessing device 2 detects an object in a target area based onthree-dimensional distance information received from the informationacquiring device 1, and controls the TV 3 based on a detection result.

For instance, the information processing device 2 detects a person basedon received three-dimensional distance information, and detects a motionof the person based on a change in the three-dimensional distanceinformation. For instance, in the case where the information processingdevice 2 is a controller for controlling a TV, the informationprocessing device 2 is installed with an application program operable todetect a gesture of a user based on received three-dimensional distanceinformation, and output a control signal to the TV 3 in accordance withthe detected gesture. In this case, the user is allowed to control theTV 3 to execute a predetermined function such as switching the channelor turning up/down the volume by performing a certain gesture whilewatching the TV 3.

Further, for instance, in the case where the information processingdevice 2 is a game machine, the information processing device 2 isinstalled with an application program operable to detect a motion of auser based on received three-dimensional distance information, andoperate a character on a TV screen in accordance with the detectedmotion to change the match status of a game. In this case, the user isallowed to play the game as if the user himself or herself is thecharacter on the TV screen by performing a certain action while watchingthe TV 3.

FIG. 2 is a diagram showing an arrangement of the information acquiringdevice 1 and the information processing device 2.

The information acquiring device 1 is provided with a projection opticalsystem 11 and a light receiving optical system 12, which constitute anoptical section. The projection optical system 11 and the lightreceiving optical system 12 are disposed in the information acquiringdevice 1 side by side in X-axis direction.

The projection optical system 11 is provided with a laser light source111, a collimator lens 112, an aperture 113, and a diffractive opticalelement (DOE) 114. Further, the light receiving optical system 12 isprovided with an aperture 121, an imaging lens 122, a filter 123, and aCMOS image sensor 124. In addition to the above, the informationacquiring device 1 is provided with a CPU (Central Processing Unit) 21,a laser driving circuit 22, an image signal processing circuit 23, aninput/output circuit 24, and a memory 25, which constitute a circuitsection.

The laser light source 111 outputs laser light in a narrow wavelengthband of or about 830 nm. The collimator lens 112 converts the laserlight emitted from the laser light source 111 into parallel light. Theaperture 113 adjusts a light flux cross section of laser light into apredetermined shape. The DOE 114 has a diffraction pattern on anincident surface thereof. Laser light entered to the DOE 114 through theaperture 113 is converted into laser light having a dot pattern by adiffractive action of the diffraction pattern, and is irradiated onto atarget area.

Laser light reflected on the target area is entered to the imaging lens122 through the aperture 121. The aperture 121 converts external lightinto convergent light in accordance with the F-number of the imaginglens 122. The imaging lens 122 condenses the light entered through theaperture 121 on the CMOS image sensor 124.

The filter 123 is a band-pass filter which transmits light in awavelength band including the emission wavelength band (in the range ofabout 830 nm) of the laser light source 111, and blocks light in avisible light wavelength band. The CMOS image sensor 124 receives lightcondensed on the imaging lens 122, and outputs a signal (electriccharge) in accordance with a received light amount to the image signalprocessing circuit 23 pixel by pixel. In this example, the CMOS imagesensor 124 is configured in such a manner that the output speed ofsignals to be outputted from the CMOS image sensor 124 is set high sothat a signal (electric charge) at each pixel can be outputted to theimage signal processing circuit 23 with high response from a lightreceiving timing at each pixel.

The CPU 21 controls the parts of the information acquiring device 1 inaccordance with a control program stored in the memory 25. By thecontrol program, the CPU 21 has functions of a laser controller 21 a forcontrolling the laser light source 111 and a three-dimensional distancecalculator 21 b for generating three-dimensional distance information.

The laser driving circuit 22 drives the laser light source 111 inaccordance with a control signal from the CPU 21. The image signalprocessing circuit 23 controls the CMOS image sensor 124 to successivelyread signals (electric charges) from the pixels, which have beengenerated in the CMOS image sensor 124, line by line. Then, the imagesignal processing circuit 23 outputs the read signals successively tothe CPU 21. The CPU 21 calculates a distance from the informationacquiring device 1 to each portion of an object to be detected, by aprocessing to be implemented by the three-dimensional distancecalculator 21 b, based on the signals (image signals) to be suppliedfrom the image signal processing circuit 23. The input/output circuit 24controls data communications with the information processing device 2.

The information processing device 2 is provided with a CPU 31, aninput/output circuit 32, and a memory 33. The information processingdevice 2 is provided with e.g. an arrangement for communicating with theTV 3, or a drive device for reading information stored in an externalmemory such as a CD-ROM and installing the information in the memory 33,in addition to the arrangement shown in FIG. 2. The arrangements of theperipheral circuits are not shown in FIG. 2 to simplify the description.

The CPU 31 controls each of the parts of the information processingdevice 2 in accordance with a control program (application program)stored in the memory 33. By the control program, the CPU 31 has afunction of an object detector 31 a for detecting an object in an image.The control program is e.g. read from a CD-ROM by an unillustrated drivedevice, and is installed in the memory 33.

For instance, in the case where the control program is a game program,the object detector 31 a detects a person and a motion thereof in animage based on three-dimensional distance information supplied from theinformation acquiring device 1. Then, the information processing device2 causes the control program to execute a processing for operating acharacter on a TV screen in accordance with the detected motion.

Further, in the case where the control program is a program forcontrolling a function of the TV 3, the object detector 31 a detects aperson and a motion (gesture) thereof in the image based onthree-dimensional distance information supplied from the informationacquiring device 1. Then, the information processing device 2 causes thecontrol program to execute a processing for controlling a predeterminedfunction (such as switching the channel or adjusting the volume) of theTV 3 in accordance with the detected motion (gesture).

The input/output circuit 32 controls data communication with theinformation acquiring device 1.

FIG. 3A is a diagram schematically showing an irradiation state of laserlight onto a target area. FIG. 3B is a diagram schematically showing alight receiving state of laser light on the CMOS image sensor 124. Tosimplify the description, FIG. 3B shows a light receiving state in thecase where a flat plane (screen) is disposed on a target area.

The projection optical system 11 irradiates a target area with laserlight having a dot pattern (hereinafter, the entirety of the laser lighthaving the dot pattern is called as “DP light”).

FIG. 3A shows a light flux area of DP light by a solid-line frame. Inthe light flux of DP light, dot areas (hereinafter, simply called as“dots”) in which the intensity of laser light is increased by adiffractive action of the DOE 114 locally appear in accordance with thedot pattern by the diffractive action of the DOE 114.

To simplify the description, in FIG. 3A, a light flux of DP light isdivided into segment areas arranged in the form of a matrix. Dotslocally appear with a unique pattern in each segment area. The dotappearance pattern in a certain segment area differs from the dotappearance patterns in all the other segment areas. With thisconfiguration, each segment area is identifiable from all the othersegment areas by a unique dot appearance pattern of the segment area.

When a flat plane (screen) exists in a target area, the segment areas ofDP light reflected on the flat plane are distributed in the form of amatrix on the CMOS image sensor 124, as shown in FIG. 3B. For instance,light of a segment area S0 in the target area shown in FIG. 3A isentered to a segment area Sp shown in FIG. 3B, on the CMOS image sensor124. In FIG. 3B, a light flux area of DP light is also indicated by asolid-line frame, and to simplify the description, a light flux of DPlight is divided into segment areas arranged in the form of a matrix inthe same manner as shown in FIG. 3A.

The three-dimensional distance calculator 21 b is operable to detect aposition of each segment area on the CMOS image sensor 124 for detectinga distance to a position of an object to be detected corresponding tothe segment area, based on the detected position of the segment area,using a triangulation method. The details of the above detection methodis disclosed in e.g. pp. 1279-1280, the 19th Annual ConferenceProceedings (Sep. 18-20, 2001) by the Robotics Society of Japan.

FIGS. 4A, 4B are diagrams schematically showing a reference templategeneration method for use in the aforementioned distance detection.

As shown in FIG. 4A, at the time of generating a reference template, areflection plane RS perpendicular to Z-axis direction is disposed at aposition away from the projection optical system 11 by a predetermineddistance Ls. The temperature of the laser light source 111 is retainedat a predetermined temperature (reference temperature). Then, DP lightis emitted from the projection optical system 11 for a predeterminedtime Te in the above state. The emitted DP light is reflected on thereflection plane RS, and is entered to the CMOS image sensor 124 in thelight receiving optical system 12. By performing the above operation, anelectrical signal at each pixel is outputted from the CMOS image sensor124. The value (pixel value) of the electrical signal at each outputtedpixel is expanded in the memory 25 shown in FIG. 2.

As shown in FIG. 4B, a reference pattern area for defining anirradiation area of DP light on the CMOS image sensor 124 is set, basedon the pixel values expanded in the memory 25. Further, the referencepattern area is divided into segment areas in the form of a matrix. Asdescribed above, dots locally appear with a unique pattern in eachsegment area. Accordingly, each segment area has a different pattern ofpixel values. Each one of the segment areas has the same size as all theother segment areas.

The reference template is configured in such a manner that pixel valuesof the pixels included in each segment area set on the CMOS image sensor124 are correlated to the segment area.

Specifically, the reference template includes information relating tothe position of a reference pattern area on the CMOS image sensor 124,pixel values of all the pixels included in the reference pattern area,and information for use in dividing the reference pattern area intosegment areas. The pixel values of all the pixels included in thereference pattern area correspond to a dot pattern of DP light includedin the reference pattern area. Further, pixel values of pixels includedin each segment area are acquired by dividing a mapping area on pixelvalues of all the pixels included in the reference pattern area intosegment areas. The reference template may retain pixel values of pixelsincluded in each segment area, for each segment area.

The reference template thus configured is stored in the memory 25 shownin FIG. 2 in a non-erasable manner. The reference template stored in thememory 25 is referred to in calculating a distance from the projectionoptical system 11 to each portion of an object to be detected.

For instance, in the case where an object is located at a positionnearer to the distance Ls shown in FIG. 4A, DP light (DPn) correspondingto a segment area Sn on the reference pattern is reflected on theobject, and is entered to an area Sn′ different from the segment areaSn. Since the projection optical system 11 and the light receivingoptical system 12 are adjacent to each other in X-axis direction, thedisplacement direction of the area Sn′ relative to the segment area Snis aligned in parallel to X-axis. In the case shown in FIG. 4A, sincethe object is located at a position nearer to the distance Ls, the areaSn′ is displaced relative to the segment area Sn in plus X-axisdirection. If the object is located at a position farther from thedistance Ls, the area Sn′ is displaced relative to the segment area Snin minus X-axis direction.

A distance Lr from the projection optical system 11 to a portion of theobject irradiated with DP light (DPn) is calculated, using the distanceLs, and based on a displacement direction and a displacement amount ofthe area Sn′ relative to the segment area Sn, by a triangulation method.A distance from the projection optical system 11 to a portion of theobject corresponding to the other segment area is calculated in the samemanner as described above.

In performing the distance calculation, it is necessary to detect towhich position, a segment area Sn of the reference template hasdisplaced at the time of actual measurement. The detection is performedby performing a matching operation between a dot pattern of DP lightirradiated onto the CMOS image sensor 124 at the time of actualmeasurement, and a dot pattern included in the segment area Sn.

FIGS. 5A through 5C are diagrams for describing the aforementioneddetection method. FIG. 5A is a diagram showing a state as to how areference pattern area and a segment area are set on the CMOS imagesensor 124, FIG. 5B is a diagram showing a segment area searching methodto be performed at the time of actual measurement, and FIG. 5C is adiagram showing a matching method between an actually measured dotpattern of DP light, and a dot pattern included in a segment area of areference template.

For instance, in the case where a displacement position of a segmentarea 51 at the time of actual measurement shown in FIG. 5A is searched,as shown in FIG. 5B, the segment area S1 is fed pixel by pixel in X-axisdirection in a range from P1 to P2 for obtaining a matching degreebetween the dot pattern of the segment area 51, and the actuallymeasured dot pattern of DP light, at each feeding position. In thiscase, the segment area 51 is fed in X-axis direction only on a line L1passing an uppermost segment area group in the reference pattern area.This is because, as described above, each segment area is normallydisplaced only in X-axis direction from a position set by the referencetemplate at the time of actual measurement. In other words, the segmentarea S1 is conceived to be on the uppermost line L1. By performing asearching operation only in X-axis direction as described above, theprocessing load for searching is reduced.

At the time of actual measurement, a segment area may be deviated inX-axis direction from the range of the reference pattern area, dependingon the position of an object to be detected. In view of the above, therange from P1 to P2 is set wider than the X-axis directional width ofthe reference pattern area.

At the time of detecting the matching degree, an area (comparative area)of the same size as the segment area S1 is set on the line L1, and adegree of similarity between the comparative area and the segment areaS1 is obtained. Specifically, there is obtained a difference between thepixel value of each pixel in the segment area S1, and the pixel value ofa pixel, in the comparative area, corresponding to the pixel in thesegment area S1. Then, a value Rsad which is obtained by summing up thedifference with respect to all the pixels in the comparative area isacquired as a value representing the degree of similarity.

For instance, as shown in FIG. 5C, in the case where pixels of m columnsby n rows are included in one segment area, there is obtained adifference between a pixel value T(i, j) of a pixel at i-th column, j-throw in the segment area, and a pixel value I(i, j) of a pixel at i-thcolumn, j-th row in the comparative area. Then, a difference is obtainedwith respect to all the pixels in the segment area, and the value Rsadis obtained by summing up the differences. In other words, the valueRsad is calculated by the following formula.

$\begin{matrix}{{Rsad} = {\sum\limits_{j = 1}^{n}\;{\sum\limits_{i = 1}^{m}\;{{{I( {i,j} )} - {T( {i,j} )}}}}}} & (1)\end{matrix}$

As the value Rsad is smaller, the degree of similarity between thesegment area and the comparative area is high.

At the time of a searching operation, the comparative area issequentially set in a state that the comparative area is displaced pixelby pixel on the line L1. Then, the value Rsad is obtained for all thecomparative areas on the line L1. A value Rsad smaller than a thresholdvalue is extracted from among the obtained values Rsad. In the casewhere there is no value Rsad smaller than the threshold value, it isdetermined that the searching operation of the segment area S1 hasfailed. In this case, a comparative area having a smallest value amongthe extracted values Rsad is determined to be the area to which thesegment area S1 has moved. The segment areas other than the segment areaS1 on the line L1 are searched in the same manner as described above.Likewise, segment areas on the other lines are searched in the samemanner as described above by setting a comparative area on the otherline.

In the case where the displacement position of each segment area issearched from the dot pattern of DP light acquired at the time of actualmeasurement in the aforementioned manner, as described above, thedistance to a portion of the object to be detected corresponding to eachsegment area is obtained based on the displacement positions, using atriangulation method.

It is not always the case that DP light is irradiated onto the CMOSimage sensor 124 in such a state that each dot of a dot pattern of DPlight acquired at the time of actual measurement is located within anarea of a corresponding pixel on the CMOS image sensor 124. DP light maybe frequently irradiated onto the CMOS image sensor 124 in such a statethat a dot overlaps two pixels or four pixels on the CMOS image sensor124. A dot is shifted horizontally (X-axis direction), depending on adistance to an object to be detected. Accordingly, as shown in FIG. 5C,DP light may be irradiated onto the CMOS image sensor 124 in such astate that a dot overlaps two pixels horizontally (X-axis direction).Normally, a dot does not overlap pixels vertically (Y-axis direction).However, a dot may be shifted vertically (Y-axis direction) resultingfrom e.g. a change in the characteristic of the DOE 114 or a variationin the emission wavelength of the laser light source 111 based on atemperature change. In such a case, a dot may overlap two pixelsvertically (Y-axis direction).

If a dot overlaps plural pixels as described above, signals areconcurrently outputted from the pixels adjacent to each other. As aresult, a border may disappear from a pixel pattern of outputtingsignals. This may degrade the matching precision between a segment areaand a comparative area.

FIGS. 6A through 6F are diagrams showing a dot pattern setting example(comparative example). The dot pattern may be modified by adjusting thediffractive pattern of the DOE 114.

In FIGS. 6A through 6F, one pixel corresponds to one square. Further,black circles in upper diagrams of FIGS. 6A through 6C indicate a dot(light), and the intensity of an output value (pixel value) of eachpixel is expressed by a shading state of squares in lower diagrams ofFIGS. 6D through 6F. In lower diagrams of FIGS. 6D through 6F, a whitesquare indicates that the pixel value is zero, and a black squareindicates a pixel value (pixel value=H) in the case where one dot isentered only in one pixel. The size of a dot is set smaller than thearea of one pixel.

Here after, the border means a section including the pixel(s) with thesame pixel value(s) which is distinct from the pixel value of the pixeladjacent to the section.

In the setting example shown in FIGS. 6A through 6F, the pitch of dotsin X-axis direction and in Y-axis direction is set to 2 pixels. FIGS.6A, 6B and 6C show the relations between dots and pixels on the CMOSimage sensor 124, and FIGS. 6D, 6E and 6F respectively show states of asignal output value (pixel value) of each pixel in the case where dotsare irradiated in the states shown in FIGS. 6A, 6B and 6C. FIGS. 6B and6E show an irradiation state of dots and a state of pixel values insegment areas at the time of generating a reference template; and FIGS.6A, 6D and FIGS. 6C, 6F show irradiation states of dots and states ofpixel values in the case where the dot pattern shown in FIG. 6B isirradiated onto predetermined comparative areas at the time of actualmeasurement.

In the case where a dot is located within one pixel, as shown in FIG.6B, a signal of a pixel value H is outputted from a corresponding pixelas shown in FIG. 6E.

On the other hand, at the time of actual measurement, as shown in FIG.6C, if the dot pattern is deviated with respect to the comparative areasin left direction (minus X-axis direction) by half pixel, as shown inFIG. 6F, a signal of a pixel value H/2 is outputted from all the pixelsin each of the second, fourth, sixth and eighth rows from the uppermostrow. In this case, there is no border (a section of a pixel having apixel value of zero) in a pixel pattern of outputting signals, in eachof the second, fourth, sixth and eighth rows from the uppermost row. Asa result, it is difficult to perform a matching operation between thepixel value patterns shown in FIGS. 6E and 6F by comparison.

Further, at the time of actual measurement, as shown in FIG. 6A if thedot pattern is deviated with respect to the comparative areas in leftdirection (minus X-axis direction) and in upper direction (plus Y-axisdirection) by half pixel, as shown in FIG. 6D, a signal of a pixel valueH/4 is outputted from all the pixels. In this case, there is no borderin a pixel pattern of outputting signals with respect to all thecomparative areas. As a result, it is more difficult to perform amatching operation between the pixel value patterns shown in FIGS. 6Eand 6D by comparison.

FIGS. 7A through 7F are diagrams showing another dot pattern settingexample (comparative example). FIGS. 7A through 7F respectivelycorrespond to FIGS. 6A through 6F. In this setting example, the size ofone dot is also set smaller than the area of one pixel. Further, in thissetting example, the pitch of dots in X-axis direction is set to 1 pixelor 2 pixels, and the pitch of dots in Y-axis direction is set to 2pixels.

At the time of actual measurement, as shown in FIG. 7C, if the dotpattern is deviated with respect to the comparative areas in leftdirection (minus X-axis direction) by half pixel, as shown in FIG. 7F,only one pixel has a pixel value H, and the rest of the pixels have apixel value H/2 in each of the second, fourth, sixth and eighth rowsfrom the uppermost row. In this case, there remain some borders in thepixel pattern of each of the second, fourth, sixth and eighth rows fromthe uppermost row, as compared with the case shown in FIG. 6F. However,the number of borders in the pixel pattern of each of the second,fourth, sixth and eighth rows is significantly small, as compared withthe case shown in FIG. 7E. Accordingly, it is difficult to perform amatching operation between the pixel value patterns shown in FIGS. 7Eand 7F by comparison.

Further, at the time of actual measurement, as shown in FIG. 7A, if thedot pattern is deviated with respect to the comparative areas in leftdirection (minus X-axis direction) and in upper direction (plus Y-axisdirection) by half pixel, as shown in FIG. 7D, only one pixel has apixel value H/2, and the rest of the pixels have a pixel value H/4 ineach row. In this case, there remain some borders in the pixel patternof each row, as compared with the case shown in FIG. 6D. However, thenumber of borders in the pixel pattern of each of the second, fourth,sixth and eighth rows is significantly small, as compared with the caseshown in FIG. 7E. Further, the pixel value patterns in the first, third,fifth and seventh rows from the uppermost row differ from each otherbetween FIG. 7D and FIG. 7E. Accordingly, it is difficult to perform amatching operation between the pixel value patterns shown in FIGS. 7Dand 7E by comparison.

FIGS. 8A through 8F are diagrams showing a dot pattern setting examplein the embodiment. In this arrangement, it is also possible to set thedot pattern as shown in FIGS. 8A through 8F by adjusting the diffractivepattern of the DOE 114.

FIGS. 8A through 8F respectively correspond to FIGS. 6A through 6F. Inthis setting example, the size of one dot is also set smaller than thearea of one pixel. Further, in this setting example, the pitch of dotsin X-axis direction is set to 2.5 pixels, and the pitch of dots inY-axis direction is set to 2 pixels.

At the time of actual measurement, as shown in FIG. 8C, if the dotpattern is deviated with respect to the comparative areas in leftdirection (minus X-axis direction) by half pixel, as shown in FIG. 8F,three borders having a pixel value of zero are formed in the pixel valuepattern in each of the second, fourth, sixth and eight rows from theuppermost row. On the other hand, three borders having a pixel value ofzero are also formed in the pixel value pattern in each of the second,fourth, sixth and eight rows from the uppermost row in FIG. 8E. Thus,the number of borders is the same as each other between FIG. 8E and FIG.8F. Further, the positions of the borders coincide with each other orare displaced from each other by a distance corresponding to about onepixel between FIGS. 8E and 8F. Thus, the pixel value pattern shown inFIG. 8F is analogous to the pixel value pattern shown in FIG. 8E.Accordingly, it is easy to perform a matching operation between thepixel value patterns shown in FIGS. 8E and 8F by comparison.

Further, at the time of actual measurement, as shown in FIG. 8A, if thedot pattern is deviated with respect to the comparative areas in leftdirection (minus X-axis direction) and in upper direction (plus Y-axisdirection) by half pixel, as shown in FIG. 8D, three borders having apixel value of zero are formed in the pixel value pattern in each of thesecond, fourth, sixth and eight rows from the uppermost row. On theother hand, three borders having a pixel value of zero are also formedin the pixel value pattern in each of the second, fourth, sixth andeighth rows in FIG. 8E. Thus, the number of borders is the same as eachother between FIG. 8E and FIG. 8D. Further, the positions of the bordersin each of the second, fourth, sixth and eight rows coincide with eachother or are displaced by a distance corresponding to about one pixelbetween FIGS. 8E and 8D. Thus, the pixel value pattern shown in FIG. 8Dis analogous to the pixel value pattern shown in FIG. 8E.

Further, comparing the first, third, fifth and seventh rows between FIG.8E and FIG. 8D, a degree of difference between FIGS. 8E and 8D is small,as compared with the difference in the pixel value pattern in the first,third, fifth and seventh rows between FIG. 6E and FIG. 6D, or thedifference in the pixel value pattern in the first, third, fifth andseventh rows between FIG. 7E and FIG. 7D. Accordingly, it is conceivedthat the difference in the pixel value pattern in the first, third,fifth and seventh rows between FIG. 8E and FIG. 8D does notsignificantly affect the matching determination between the pixel valuepatterns shown in FIGS. 8E and 8D.

As described above, in the aforementioned setting example of theembodiment, even if a dot pattern is deviated with respect to thecomparative areas in left direction (minus X-axis direction) and inupper direction (plus Y-axis direction) by half pixel, it is easy toperform a matching operation between the pixel value patterns shown inFIGS. 8E and 8D.

FIGS. 9A through 9F are diagrams showing another dot pattern settingexample in the embodiment. FIGS. 9A through 9F respectively correspondto FIGS. 6A through 6F. In this setting example, the size of one dot isalso set smaller than the area of one pixel. Further, in this settingexample, the pitch of dots in X-axis direction is set to 2.5 pixels, andthe pitch of dots in Y-axis direction is also set to 2.5 pixels.

At the time of actual measurement, as shown in FIG. 9C, if the dotpattern is deviated with respect to the comparative areas in leftdirection (minus X-axis direction) by half pixel, as shown in FIG. 9F,three borders having a pixel value of zero are formed in the pixel valuepattern in each of the first, second, fourth, sixth and seventh rowsfrom the uppermost row. On the other hand, three borders having a pixelvalue of zero are also formed in the pixel value pattern in each of thefirst, second, fourth, sixth and seventh rows in FIG. 9E. Thus, thenumber of border s is the same as each other between FIG. 9E and FIG.9F. Further, the positions of the borders coincide with each other orare displaced from each other by a distance corresponding to about onepixel between FIGS. 9E and 9F. Thus, the pixel value pattern shown inFIG. 9F is analogous to the pixel value pattern shown in FIG. 9E.Accordingly, it is easy to perform a matching operation between thepixel value patterns shown in FIGS. 9E and 9F by comparison.

Further, at the time of actual measurement, as shown in FIG. 9A, if thedot pattern is deviated with respect to the comparative areas in leftdirection (minus X-axis direction) and in upper direction (plus Y-axisdirection) by half pixel, as shown in FIG. 9D, three borders having apixel value of zero are formed in the pixel value pattern in each of thefirst, fourth and sixth rows from the uppermost row. On the other hand,three borders having a pixel value of zero are also formed in the pixelvalue pattern in each of the first, fourth and sixth rows in FIG. 9E.Thus, the number of borders is the same as each other between FIG. 9Eand FIG. 9D. Further, the positions of the borders in each of the first,fourth and sixth rows coincide with each other or are displaced fromeach other by a distance corresponding to about one pixel between FIGS.9E and 9D. Furthermore, the pixel value patterns in the fifth and eightrows coincide with each other between FIGS. 9E and 9D. Thus, the pixelvalue pattern shown in FIG. 9D is analogous to the pixel value patternshown in FIG. 9E.

Further, comparing the second and seventh rows between FIG. 9E and FIG.9D, a degree of difference between FIGS. 9E and 9D is small, as comparedwith the difference in the pixel value pattern in the first, third,fifth and seventh rows between FIG. 6E and FIG. 6D, or the difference inthe pixel value pattern in the first, third, fifth and seventh rowsbetween FIG. 7E and FIG. 7D. Accordingly, it is conceived that thedifference in the pixel value pattern in the second and seventh rowsbetween FIG. 9E and FIG. 9D does not significantly affect the matchingdetermination between the pixel value patterns shown in FIGS. 9E and 9D.

As described above, in the aforementioned setting example of theembodiment, even if a dot pattern is deviated with respect to thecomparative areas in left direction (minus X-axis direction) and inupper direction (plus Y-axis direction) by half pixel, it is easy toperform a matching operation between the pixel value patterns shown inFIGS. 9E and 9D.

In the setting example shown in FIGS. 9A through 9F, as is clear fromreferring to FIGS. 9E, 9D and 9F, there exist three or four rows, inwhich the pixel value of all the pixels is zero, and the pixel valuepattern is comparted in Y-axis direction, as well as in X-axisdirection, by these rows. In this example, the number of borders inY-axis direction is the same (three) in FIGS. 9E, 9D and 9F. Further,the positions of the borders in Y-axis direction coincide with eachother between FIG. 9E and FIG. 9F, and coincide with each other or aredisplaced from each other by a distance corresponding to one pixelbetween FIGS. 9E and 9D. Forming borders in a pixel value pattern inY-axis direction as well as in X-axis direction is advantageous inperforming a matching operation between pixel value patterns, andenhancing the searching precision of a segment area.

FIGS. 10A through 10F are diagrams showing yet another dot patternsetting example in the embodiment. FIGS. 10A through 10F respectivelycorrespond to FIGS. 6A through 6F. In this setting example, the size ofone dot is also set smaller than the area of one pixel. Further, in thissetting example, the pitch of dots in X-axis direction is set to 3pixels, and the pitch of dots in Y-axis direction is set to 2 pixels.

At the time of actual measurement, as shown in FIG. 10C, if the dotpattern is deviated with respect to the comparative areas in leftdirection (minus X-axis direction) by half pixel, as shown in FIG. 10F,three borders having a pixel value of zero are formed in the pixel valuepattern in each of the second, fourth, sixth and eighth rows from theuppermost row. On the other hand, three borders having a pixel value ofzero are also formed in the pixel value pattern in each of the second,fourth, sixth and eighth rows in FIG. 10E. Thus, the number of bordersis the same as each other between FIG. 10E and FIG. 10F. Further, allthe positions of the borders in each of the second, fourth, sixth andeighth rows in FIG. 10F are included in the positions of the borders ineach of the second, fourth, sixth and eighth rows in FIG. 10E. Thus, thepixel value pattern shown in FIG. 10F is analogous to the pixel valuepattern shown in FIG. 10E. Accordingly, it is easy to perform a matchingoperation between the pixel value patterns shown in FIGS. 10E and 10F bycomparison.

At the time of actual measurement, as shown in FIG. 10A, if the dotpattern is deviated with respect to the comparative areas in leftdirection (minus X-axis direction) and in upper direction (plus Y-axisdirection) by half pixel, as shown in FIG. 10D, three borders having apixel value of zero are formed in the pixel value pattern in each of thesecond, fourth, sixth and eighth rows from the uppermost row. On theother hand, three borders having a pixel value of zero are also formedin the pixel value pattern in each of the second, fourth, sixth andeighth rows in FIG. 10E. Thus, the number of borders is the same as eachother between FIG. 10E and FIG. 10D. Further, all the positions of theborders in each of the second, fourth, sixth and eighth rows in FIG. 10Dare included in the positions of the borders in each of the second,fourth, sixth and eighth rows in FIG. 10E. Thus, the pixel value patternshown in FIG. 10D is very analogous to the pixel value pattern shown inFIG. 10E.

Further, comparing the first, third, fifth and seventh rows between FIG.10E and FIG. 10D, a degree of difference between FIGS. 10E and 10D issmall, as compared with the difference in the pixel value pattern in thefirst, third, fifth and seventh rows between FIG. 6E and FIG. 6D, or thedifference in the pixel value pattern in the first, third, fifth andseventh rows between FIG. 7E and FIG. 7D. Accordingly, it is conceivedthat the difference in the pixel value pattern in the first, third,fifth and seventh rows between FIG. 10E and FIG. 10D does notsignificantly affect the matching determination between the pixel valuepatterns shown in FIGS. 10E and 10D.

As described above, in the aforementioned setting example of theembodiment, even if a dot pattern is deviated with respect to thecomparative areas in left direction (minus X-axis direction) and inupper direction (plus Y-axis direction) by half pixel, it is easy toperform a matching operation between the pixel value patterns shown inFIGS. 10E and 10D.

Between the pixel value patterns shown in FIGS. 10E and 10F, the numberof pixels whose pixel values do not coincide with each other is five inthe second row, six in the fourth row, four in the sixth row, and fivein the eighth row; namely, the number is twenty in total. On the otherhand, between the pixel value patterns shown in FIGS. 8E and 8F, thenumber of pixels whose pixel values do not coincide with each other issix in the second row, six in the fourth row, six in the sixth row, andsix in the eighth row; namely, the number is twenty-four in total. Thus,the number of pixels whose pixel values do not coincide with each otheris smaller in the pixel value patterns shown in FIGS. 10E and 10F thanin the pixel value patterns shown in FIGS. 8E and 8F, by four. Further,a pixel value difference between two pixels whose pixel values do notcoincide with each other is H/2 in all the cases. Thus, it is conceivedthat the matching detection precision is higher in the dot patternsshown in FIGS. 10A through 10F than in the dot patterns shown in FIGS.8A through 8F. In this aspect, it is further preferable to set the pitchof dots to 3 pixels, rather than 2.5 pixels.

FIGS. 11A through 11F are diagrams showing still another dot patternsetting example in the embodiment. FIGS. 11A through 11F respectivelycorrespond to FIGS. 6A through 6F. In this setting example, the size ofone dot is also set smaller than the area of one pixel. Further, in thissetting example, the pitch of dots in X-axis direction is set to 3.5pixels, and the pitch of dots in Y-axis direction is set to 2 pixels.

Comparing the matching degree of the pixel value patterns shown in FIGS.11E and 11F, and the matching degree of the pixel value patterns shownin FIGS. 10E and 10F, the matching degrees are substantially the same aseach other. Specifically, between the pixel value patterns shown inFIGS. 11E and 11F, the number of pixels whose pixel values do notcoincide with each other is five in the second row, six in the fourthrow, four in the sixth row, and five in the eighth row; namely, thenumber is twenty in total. On the other hand, between the pixel valuepatterns shown in FIGS. 10E and 10F, the number of pixels whose pixelvalues do not coincide with each other is five in the second row, six inthe fourth row, four in the sixth row, and five in the eighth row;namely, the number is twenty in total. Thus, the number of pixels whosepixel values do not coincide with each other is the same as each otherbetween the pixel value patterns shown in FIGS. 11E and 11F and thepixel value patterns shown in FIGS. 10E and 10F. Further, a pixel valuedifference between two pixels whose pixel values do not coincide witheach other is H/2 in all the cases. Thus, it is conceived that thematching detection precision is substantially the same as each otherbetween the dot patterns shown in FIGS. 11A through 11F and the dotpatterns shown in FIGS. 10A through 10F.

In this aspect, it is conceived that the dot pattern searching precisionsubstantially does not change, even if the pitch of dots in X-axisdirection is set to 3.5 pixels or larger. Contrary to the expectation,if the pitch of dots is increased, the number of dots to be included inone segment area is reduced. As a result, it is difficult to obtain adifference in the value Rsad (see the aforementioned formula (1))representing a degree of similarity, which may degrade the dot patternsearching precision. In view of the above, it is desirable to set thepitch of dots in X-axis direction in the range of from about 2.5 pixelsto about 3.5 pixels, and more preferable to set the pitch to about 3.0pixels. It is preferable to set the pitch of dots in X-axis direction to2.5 pixels in order to include a larger number of dots in one segmentarea.

As described above, according to the embodiment, it is possible toimplement an information acquiring device that enables to enhance thedot pattern detection precision, and an object detecting device loadedwith the information acquiring device. Further, the aforementionedeffect can be realized by a very simplified method of adjusting thepitch of dots.

The embodiment of the invention has been described as above. Theinvention is not limited to the foregoing embodiment, and the embodimentof the invention may be changed or modified in various ways other thanthe above.

For instance, in the embodiment, the segment areas are set withoutoverlapping each other, as shown in FIG. 4B. Alternatively, segmentareas may be set in such a manner that upper and lower segment areaspartially overlap each other. Further alternatively, segment areas maybe set in such a manner that left and right segment areas partiallyoverlap each other in the form of a matrix. In the modifications,however, the pitch of dots within each segment area is adjusted to beequal to or larger than 2.5 pixels.

Further alternatively, the shape of the reference pattern area may be asquare shape or other shape, in addition to the rectangular shape asdescribed in the embodiment.

In the embodiment, the CMOS image sensor 124 is used as a lightreceiving element. Alternatively, a CCD image sensor may be used.

The embodiment of the invention may be changed or modified in variousways as necessary, as far as such changes and modifications do notdepart from the scope of the claims of the invention hereinafterdefined.

1. An information acquiring device for acquiring information on a targetarea using light, comprising: a light source which emits light of apredetermined wavelength band; a projection optical system whichprojects the light emitted from the light source toward the target areawith a predetermined dot pattern; and a light receiving element whichreceives reflected light reflected on the target area for outputting asignal, wherein the projection optical system projects the light towardthe target area in such a manner that a dot of a reference pattern ofthe light to be received by the light receiving element has a pitchequal to or larger than 2.5 pixels at least in an alignment direction inwhich the light source and the light receiving element are aligned. 2.The information acquiring device according to claim 1, wherein theprojection optical system projects the light toward the target area insuch a manner that a dot of a reference pattern of the light to bereceived by the light receiving element has a pitch equal to or largerthan 2.5 pixels in an alignment direction in which the light source andthe light receiving element are aligned, and in a directionperpendicular to the alignment direction.
 3. The information acquiringdevice according to claim 1, wherein the pitch in the alignmentdirection is set to 2.5 to 3.5 pixels.
 4. The information acquiringdevice according to claim 3, wherein the pitch in the alignmentdirection is set to 2.5 pixels.
 5. The information acquiring deviceaccording to claim 3, wherein the pitch in the alignment direction isset to 3.0 pixels.
 6. The information acquiring device according toclaim 2, wherein the pitch in the alignment direction is set to 2.5 to3.5 pixels.
 7. The information acquiring device according to claim 6,wherein the pitch in the alignment direction is set to 2.5 pixels. 8.The information acquiring device according to claim 6, wherein the pitchin the alignment direction is set to 3.0 pixels.
 9. An object detectingdevice, comprising: an information acquiring device which acquiresinformation on a target area using light, the information acquiringdevice including: a light source which emits light of a predeterminedwavelength band; a projection optical system which projects the lightemitted from the light source toward the target area with apredetermined dot pattern; and a light receiving element which receivesreflected light reflected on the target area for outputting a signal,wherein the projection optical system projects the light toward thetarget area in such a manner that a dot of a reference pattern of thelight to be received by the light receiving element has a pitch equal toor larger than 2.5 pixels at least in an alignment direction in whichthe light source and the light receiving element are aligned.
 10. Theobject detecting device according to claim 9, wherein the projectionoptical system projects the light toward the target area in such amanner that a dot of a reference pattern of the light to be received bythe light receiving element has a pitch equal to or larger than 2.5pixels in an alignment direction in which the light source and the lightreceiving element are aligned, and in a direction perpendicular to thealignment direction.
 11. The object detecting device according to claim9, wherein the pitch in the alignment direction is set to 2.5 to 3.5pixels.
 12. The object detecting device according to claim 11, whereinthe pitch in the alignment direction is set to 2.5 pixels.
 13. Theobject detecting device according to claim 11, wherein the pitch in thealignment direction is set to 3.0 pixels.
 14. The object detectingdevice according to claim 10, wherein the pitch in the alignmentdirection is set to 2.5 to 3.5 pixels.
 15. The object detecting deviceaccording to claim 14, wherein the pitch in the alignment direction isset to 2.5 pixels.
 16. The object detecting device according to claim14, wherein the pitch in the alignment direction is set to 3.0 pixels.